1) Field of the Disclosure
The disclosure relates generally to methods and systems for processing shape memory alloy (SMA) material, such that when the SMA is cycled, or transforms, it produces a racking motion. The disclosure further relates to mechanical actuators having shape memory alloys imparted with the racking motion and a method of using the mechanical actuators to influence or warp the shape of a structure such as an airfoil.
2) Description of Related Art
The ability to controllably twist, bend, or deform an aerodynamic surface of an air vehicle, such as a wing of an aircraft, a rotor blade of a rotorcraft, or another aerodynamic surface, during various phases of flight may significantly enhance the performance of the air vehicle. A limitation to implementing known mechanical and/or electromagnetic actuators or other devices that are designed to twist, bend, or deform a wing of an aircraft, a rotor blade of a rotorcraft, or another aerodynamic surface, is that the actuators or other devices used for this purpose must overcome the inherent structural stiffness of the material used to form the wing, rotor blade, or other aerodynamic surface.
Actuators and actuator system components made of shape memory alloys (SMA) and designed for use in air vehicles are known. Shape memory alloys (SMA) are a group of metals that have interesting thermal and mechanical properties. Shape memory alloys can exist in one of several distinct temperature-dependent phases. The most commonly utilized of these phases are the so-called martensite and austenite phases. Upon heating a shape memory alloy through a transformation temperature, the shape memory alloy changes from the martensite phase into the austenite phase. If a component made of a shape memory alloy material, for example, NiTinol, is deformed while in a martensitic state (low yield strength condition) and then heated to its transition temperature to reach an austenitic state, the shape memory alloy material of the component will resume its original (undeformed) shape. The rate of return to the original shape depends upon the amount and rate of thermal energy applied to the component. When heat is removed from the component, it will return to the martensitic state in which the component can again be deformed.
Known limitations of thermo-mechanical processing of SMA actuators and structures may include axially straining, bending strain, torsional straining. Further, known SMA actuator system components for known actuators may include SMA wires that may be trained by pulling, and SMA plates that may be trained by bending. However, actuation or shape control of surfaces by such known SMA actuator system components may be difficult to control. Moreover, the shape and size of such known SMA actuator system components may make it difficult to integrate into known actuators or other types of SMA actuators.
In addition, known SMA actuators may include SMA twist tube actuators that apply forces and torques at one or more discrete locations along an aerodynamic surface and that may be trained by twisting. The SMA material of such known SMA twist tube actuators may have a two-way shape effect to allow the twist tube actuator to twist from an original shape to a trained shape and twist back from the trained shape to the original shape. However, such known SMA twist tube actuators may require two SMA twist tube components which may require electrical power be continuously applied to the heater elements of each SMA member to maintain a specific loaded rotational position. This may add system weight and complexity as well as require excessive power.
Accordingly, there is a need in the art for improved methods and systems for shape memory alloy (SMA) structures that provide advantages over known methods and systems.